Sen. Rand Paul, R-Ky., speaks during a breakfast Wednesday hosted by the Westside Conservative Club at the Machine Shed Restaurant in a Urbandale, Iowa, near Des Moines. / Scott Olson, Getty Images

by Fredreka Schouten, USA TODAY

by Fredreka Schouten, USA TODAY

As Kentucky Sen. Rand Paul hopscotched across Iowa this week, so have video-camera-toting Democratic trackers.

Staffers with American Bridge 21st Century, a Democratic opposition research group, trailed the potential presidential candidate to an open house at the Scott County Republican headquarters in Davenport, recorded his remarks at a breakfast with conservatives in a Des Moines suburb, and transcribed every word of his interview with a local talk-radio host.

In all, three trackers monitored a total of 13 Paul appearances as he barnstormed the Hawkeye State.

The presidential election is more than two years away, but both parties' opposition-research operations are hitting high gear as mostly twentysomething trackers crisscross the country recording, cataloging and scrutinizing every utterance of all the politicians considered to be serious White House contenders in 2016.

Whenever New Jersey's Republican Gov. Chris Christie holds a town-hall meeting in his home state, an American Bridge tracker is there. When Democrat Hillary Rodham Clinton gives a speech on global policy, Republican researchers are listening in.

"We want to win races," said Brad Woodhouse, a longtime Democratic strategist who became American Bridge's president this year. "If we can win races with a macaca moment, I'll take it," he said, referring to a slur then-senator George Allen used in 2006 to refer to a young Indian-American tracker employed by his Democratic rival. Allen, who was leading in the polls at the time, lost in November.

"But those are the exceptions," Woodhouse said. "The real value is developing a narrative of a candidate over time."

American Bridge, which has both tax-exempt and super-PAC arms, can raise unlimited sums for its opposition research. It plans to spend about $18 million in this election cycle.

The group employs more than 80 people, including 43 trackers in 39 states, who monitor Republicans in Senate and governor contests this year, along with the large cast of possible White House candidates. That's more than twice the number of trackers American Bridge had on staff for the 2012 elections.

Republicans are catching up.

The GOP-aligned America Rising, started last year, already employs 68, including 26 trackers. In a Republican National Committee autopsy of Mitt Romney's 2012 defeat, the party's leaders called for a Republican counterpart to America Bridge to focus entirely on digging up dirt on Democrats.

American Rising plans to spend between $9 million and $12 million, said executive director Tim Miller.

"We're definitely making a difference," said Miller, whose trackers captured Iowa senatorial candidate Rep. Bruce Braley at a private Democratic fundraiser in Texas earlier this year when he dismissed veteran Sen. Chuck Grassley, R-Iowa, as a "farmer who â?¦ never went to law school."

He won't disclose what damaging leaks about candidates have been unearthed by his researchers. But he notes that "Republican opposition research efforts this cycle have had a lot of wins," ticking off several examples, including the plagiarism scandal that forced Sen. John Walsh, D-Mont., to abandon his Senate campaign Thursday.

Clinton, in the public eye since she became Arkansas' first lady in 1979, may be the most scrutinized politician alive. But Miller's group is scouring her recent record as secretary of State and the work of her family's foundation. The group isn't afraid to attack the Democrat from the left, either, as they search for ways to weaken her even before she decides whether to run.

In June, for instance, America Rising quickly circulated a testy exchange that Clinton had with public-radio host Terry Gross. Clinton snapped at Gross as the interviewer probed repeatedly about the evolution of Clinton's position on gay marriage. (As a presidential candidate in 2008, Clinton opposed gay marriage. Last year, she publicly backed same-sex marriage as the Supreme Court took up two significant gay rights cases.)

"Positions she held in the '80s or '90s that might have seemed politically appropriate at the time might not seem like a good idea now," Miller said.

Clinton's aides did not respond to an interview request.

Back at American Bridge's war room in Washington this week, researchers were busy scrutinizing trackers' reports of Paul's appearances in Iowa. The footage that went viral, however, wasn't recorded by their cameras. Instead, it was filmed by immigration advocates who confronted Rep. Steve King, R-Iowa, about his policies during a Monday fundraiser.

Paul, who was eating dinner at the same table, quickly moved away - leaving behind a half-eaten burger on his plate.

Paul's aides did not respond to USA TODAY requests about all the trackers watching him as he traveled the state.

In discussions on talk radio and Fox News this week, Paul said he wasn't running away from the activists' cameras, but he had to leave the table for a previously planned interview.